There are two frame structures in a long term evolution (LTE for short) system. Frame structure type 1 is applicable to frequency division duplex (FDD for short) and frequency division half-duplex. Each radio frame has a length of 10 ms, and is composed of 20 time slots, each time slot being 0.5 ms, and numbered from 0 to 19. One subframe is composed of two continuous time slots, e.g. a subframe i is composed of two continuous time slots 2i and 2i+1.
Frame structure type 2 is applicable to time division duplex (TDD for short). One radio frame has a length of 10 ms, and is composed of two half-frames, wherein the length of each half-frame is 5 ms. One half-frame is composed of 5 subframes, wherein the length of each subframe is 1 ms. A special subframe is composed of a downlink special subframe DwPTS, a guard space (GP) and an uplink special subframe UpPTS, and the total length is 1 ms. Each subframe i is composed of two time slots 2i and 2i+1, wherein the length of each time slot is 0.5 ms (15360×Ts).
In the above-mentioned two frame structures, for a normal cyclic prefix (Normal CP for short), one time slot comprises 7 symbols, wherein the length of each symbol is 66.7 μs, and a CP length of the first symbol is 5.21 μs, and lengths of the rest 6 symbols are 4.69 μs; for an extended cyclic prefix (Extended CP for short), one time slot comprises 6 symbols, wherein the CP lengths of all the symbols are 16.67 μs.
One resource element (RE for short) is an OFDM symbol in time domain, and is a subcarrier in frequency domain; one time slot comprises NsymbDL OFDM symbols; one resource block (RB for short) is composed of NsymbDL×NscRB resource elements, is 1 time slot in time domain and 180 kHz in frequency domain; when a subframe cyclic prefix is the normal cyclic prefix, one resource element is as shown in FIG. 1; one subframe corresponds to a pair of resource blocks in the same frequency domain; and a resource block pair has two mapping modes over physical resources, one is the same resource block pair frequency domain position (continuous mapping), as shown in FIG. 2, and the other is different resource block pair frequency domain positions (discrete mapping), as shown in FIG. 3.
The LTE defines the following three downlink physical control channels: a physical downlink control format indicator channel (PCFICH for short), a physical hybrid automatic retransmission request indicator channel (PHICH for short), and a physical downlink control channel (PDCCH for short).
Information carried on the PCFICH is used for indicating the number of transmitting orthogonal frequency division multiplexing (OFDM for short) symbols of the PDCCH in a subframe, is transmitted on the first OFDM symbol of the subframe, and the frequency position thereof is determined by system downlink bandwidth and cell identity (ID for short).
The PDCCH is used for bearing downlink control information (DCI for short), comprising: physical uplink shared channel (PUSCH for short) scheduling information, physical downlink shared channel (PDSCH for short) scheduling information and uplink power control information. DCI formats are divided into the following several kinds: DCI format 0, DCI format 1, DCI format 1A, DCI format 1B, DCI format 1C, DCI format 1D, DCI format 2, DCI format 2A, DCI format 2B, DCI format 2C, DCI format 3 and DCI format 3A, DCI format 4, etc., wherein there are 9 PDSCH downlink transmission modes:
The physical downlink control channel (PDCCH) is mapped onto physical resources taking a control channel element (CCE for short) as a unit. The size of one CCE is 9 resource element groups (REGs for short), i.e. 36 resource elements. One PDCCH have four aggregation levels, the four aggregation levels respectively corresponding to the case where one PDCCH occupies 1, 2, 4 or 8 CCEs, which are referred to as aggregation level 1, aggregation level 2, aggregation level 4 and aggregation level 8, which also correspond to four formats of the PDCCH. That is to say, the aggregation level represents the size of the physical resource occupied by the physical downlink control channel.
In Release (R for short) 8/9 of the LTE system, in order to measure the quality of a channel and to demodulate a received data symbol, a common reference signal (CRS for short) is designed. User equipment (UE) may perform channel measurement via the CRS, thereby supporting the UE to perform cell reselection and switching to a target cell. In LTE R10, in order to further improve the average spectrum utilization rate of a cell and the edge spectrum utilization rate of the cell and the throughput rate of each UE, two reference signals are respectively defined: a channel information reference signal (CSI-RS) and a demodulation reference signal (DMRS), wherein the CSI-RS is used for channel measurement, and the DMRS is used for downlink shared channel demodulation. The use of DMRS demodulation may use a beam method to reduce the interference between different receiving sides and different cells, and may reduce the performance decreasing due to codebook granularity, and lower the overhead of downlink control signalling to some extent.
In order to obtain larger working spectrum and system bandwidth, one direct technique is to aggregate several continuous component carriers (spectrum) distributed on different frequency bands using the carrier aggregation technology, thereby forming bandwidth which may be used by LTE-Advanced, e.g.: 100 MHz. That is to say, the aggregated spectrum is divided into n component carriers (spectrum), the spectrum in each component carrier (spectrum) being continuous. The spectrum is divided into two types: a primary component carrier (PCC) and a secondary component carrier (SCC), which are also referred to a primary cell and a secondary cell.
In an LTE R10 heterogeneous network, since different base station types have a relatively strong interference, considering the interference problem from a macro base station (Macro eNodeB) on a micro base station (Pico) and the interference problem from a home base station (Home eNodeB) on the macro base station (Macro eNodeB), LTE R11 proposes a multi-antenna transmission method based on a user-dedicated pilot frequency, which solves the interference problems. In addition, by mapping the PDCCH to a PDSCH area, the use of a frequency division multiplexing mode similar to PDSCH multiplexing may achieve frequency domain coordination of inter-cell interference.
In the LTE R11 stage, it is considered to introduce more user PDSCH areas for transmitting data. The capacity of 4 OFDM symbols at maximum configured currently may not satisfy the requirements. In order to provide a control channel with a larger capacity, there is a need to design an enhanced control channel, or there is a need to open a new resource for transmitting control information over the PDSCH resource.
At present, the specific mapping mode of the physical downlink control channel (also referred to as an enhanced physical downlink control channel (ePDCCH)) mapped onto a new resource is not determined yet, and meanwhile, the specific mapping mode needs to ensure the enhanced physical downlink control channel to obtain frequency domain diversity gain or scheduling gain; in addition, multiple ePDCCHs are centrally mapped as much as possible, so as to reduce the influence on PDSCH transmission from the resource occupied by the ePDCCHs.